我正在嘗試編寫一個程序來接收一個數字，并使用 javascript 和 html 將其映射到基于字母等級的標記。當我運行代碼時，我沒有得到任何答案。這是代碼：HTML   <h1>mapping a numerical grade to a letter grade</h1>    </header>    <div class="column1">      <div class="input">        a <input id="number1" type="number" min=" -32768" max=" 32767" />      </div>      <div class="input">        <button onclick="mapping()">enter</button>      </div>      <strong><p id="output"></p></strong>    </div>Javascript  function mapping() {  var a = parseInt(document.getElementById("number1").value);  switch (true) {    case a > 89:      answer = "A+";      break;    case a > 79:      answer = "A";      break;    case a > 74:      answer = "B+";      break;    case a > 69:      answer = "B";      break;    case a > 64:      answer = "C+";      break;    case a > 59:      answer = "C";    case a > 54:      answer = "D+";    case a > 49:      answer = "D";      break;    case a > 40:      answer = "E";      break;    default:      answer = "F";      document.getElementById("output").innerHTML = answer;}